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Simultaneous transmit and receive with digital phased arrays

October 18, 2016
  |
Conference Paper
Author:
Jonathan P. Doane
…
Published in:
6th Int. Symp. on Phased Array Systems and Technology, PAST 2016, 18-21 October 2016.
Topic:
signal processing
R&D area:
R&D group:

Summary

A new architecture is proposed for achieving Simultaneous Transmit and Receive (STAR) with a digital phased array. We demonstrate how digital beamforming and cancellation enables adjacent transmitting and receiving sub-arrays to operate simultaneously in the same frequency band without a significant reduction in performance. Our approach uses only digital signal processing techniques and does not require custom radiators or analog cancelling circuits that can increase front-end losses and add significant size, weight and cost to the array. Simulated results are presented for a 50-element array that achieves more than 160 dB of effective isolation between transmit and receive beams over a 100 MHz instantaneous band centered at 2.45 GHz.
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Summary

A new architecture is proposed for achieving Simultaneous Transmit and Receive (STAR) with a digital phased array. We demonstrate how digital beamforming and cancellation enables adjacent transmitting and receiving sub-arrays to operate simultaneously in the same frequency band without a significant reduction in performance. Our approach uses only digital signal...

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Simultaneous transmit and receive with digital phased arrays

Scalable prototyping testbed for MMW imager system

October 18, 2016
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Conference Paper
Author:
Huy T. Nguyen
…
Published in:
6th Int. Symp. on Phased Array Systems and Technology, PAST 2016, 18-21 October 2016.
Topic:
radar
R&D area:
R&D group:

Summary

A prototyping testbed for an experimental millimeter-wave multiple-imput multiple-output (MIMO) radar system for security applications in high foot-traffic areas will be presented. The system is designed for flexible operation at a 10 Hz video rate, enabled by high-speed electronic scanning and real-time signal processing. Overall imaging system costs are reduced by the use of an innovative ultra-sparse multistatic radar solution and a 3-D near-field beamforming image construction technique targeted for low-cost high-throughput GPU processors. The testbed is architected with FPGAs, GPUs, CPU storage, and networking, capable of supporting future growth in capabilities, such as interference suppression & advanced signal processing algorithms, auxiliary sensing modalities, near-sensor analytics, and integration into a system-of-systems security architecture.
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Summary

A prototyping testbed for an experimental millimeter-wave multiple-imput multiple-output (MIMO) radar system for security applications in high foot-traffic areas will be presented. The system is designed for flexible operation at a 10 Hz video rate, enabled by high-speed electronic scanning and real-time signal processing. Overall imaging system costs are reduced...

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Scalable prototyping testbed for MMW imager system

Development of a high-throughput microwave imaging system for concealed weapons detection

October 18, 2016
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Conference Paper
Author:
William F. Moulder
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Published in:
6th Int. Symp. on Phased Array Systems and Technology, PAST 2016, 18-21 October 2016.
Topic:
detection systems
R&D area:
R&D group:

Summary

A video-rate microwave imaging aperture for concealed threat detection can serve as a useful tool in securing crowded, high foot traffic environments. Realization of such a system presents two major technical challenges: 1) implementation of an electrically large antenna array for capture of a moving subject, and 2) fast image reconstruction on cost-effective computing hardware. This paper presents a hardware-efficient multistatic array design to address the former challenge, and a compatible fast imaging technique to address the latter. Prototype hardware which forms a partition of an imaging aperture is discussed. Using this hardware, it is shown that the proposed array design can be used to form high-fidelity 3D images, and that the presented image reconstruction technique can form an image of a human-sized domain in ≤ 0.1s with low cost computing hardware.
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Summary

A video-rate microwave imaging aperture for concealed threat detection can serve as a useful tool in securing crowded, high foot traffic environments. Realization of such a system presents two major technical challenges: 1) implementation of an electrically large antenna array for capture of a moving subject, and 2) fast image...

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Development of a high-throughput microwave imaging system for concealed weapons detection

Electrically switchable diffractive waveplates with metasurface aligned liquid crystals

October 17, 2016
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Journal Article
Author:
Jeffrey B. Chou
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Published in:
Opt. Express, Vol. 24, No. 21, 17 October 2016, 24265-24273.
Topic:
lithography
R&D area:
R&D group:

Summary

Diffractive waveplates and equivalent metasurfaces provide a promising path for applications in thin film beam steering, tunable lenses, and polarization filters. However, fixed metasurfaces alone are unable to be tuned electronically. By combining metasurfaces with tunable liquid crystals, we experimentally demonstrate a single layer device capable of electrically switching a diffractive waveplate design at a measured peak diffraction efficiency of 35%, and a minimum switching voltage of 10V. Furthermore, the nano-scale metasurface aligned liquid crystals are largely independent of variations in wavelength and temperature. We also present a computational analysis of the efficiency limits of liquid crystal based diffractive waveplates, and compare this analysis to experimental measurements.
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Summary

Diffractive waveplates and equivalent metasurfaces provide a promising path for applications in thin film beam steering, tunable lenses, and polarization filters. However, fixed metasurfaces alone are unable to be tuned electronically. By combining metasurfaces with tunable liquid crystals, we experimentally demonstrate a single layer device capable of electrically switching a...

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Electrically switchable diffractive waveplates with metasurface aligned liquid crystals

Multi-modal audio, video and physiological sensor learning for continuous emotion prediction

October 16, 2016
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Conference Paper
Author:
Kevin Brady
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Published in:
ACM Multimedia Conf. AVEC Workshop, 15-19 October 2016.
Topic:
biometrics
R&D area:
R&D group:

Summary

The automatic determination of emotional state from multimedia content is an inherently challenging problem with a broad range of applications including biomedical diagnostics, multimedia retrieval, and human computer interfaces. The Audio Video Emotion Challenge (AVEC) 2016 provides a well-defined framework for developing and rigorously evaluating innovative approaches for estimating the arousal and valence states of emotion as a function of time. It presents the opportunity for investigating multimodal solutions that include audio, video, and physiological sensor signals. This paper provides an overview of our AVEC Emotion Challenge system, which uses multi-feature learning and fusion across all available modalities. It includes a number of technical contributions, including the development of novel high- and low-level features for modeling emotion in the audio, video, and physiological channels. Low-level features include modeling arousal in audio with minimal prosodic-based descriptors. High-level features are derived from supervised and unsupervised machine learning approaches based on sparse coding and deep learning. Finally, a state space estimation approach is applied for score fusion that demonstrates the importance of exploiting the time-series nature of the arousal and valence states. The resulting system outperforms the baseline systems [10] on the test evaluation set with an achieved Concordant Correlation Coefficient (CCC) for arousal of 0.770 vs 0.702 (baseline) and for valence of 0.687 vs 0.638. Future work will focus on exploiting the time-varying nature of individual channels in the multi-modal framework.
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Summary

The automatic determination of emotional state from multimedia content is an inherently challenging problem with a broad range of applications including biomedical diagnostics, multimedia retrieval, and human computer interfaces. The Audio Video Emotion Challenge (AVEC) 2016 provides a well-defined framework for developing and rigorously evaluating innovative approaches for estimating the...

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Multi-modal audio, video and physiological sensor learning for continuous emotion prediction

Detecting depression using vocal, facial and semantic communication cues

October 15, 2016
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Conference Paper
Author:
James R. Williamson
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Published in:
ACM Multimedia Conf. AVEC Workshop, 15-19 October 2016.
Topic:
biometrics
R&D area:
R&D group:

Summary

Major depressive disorder (MDD) is known to result in neurophysiological and neurocognitive changes that affect control of motor, linguistic, and cognitive functions. MDD's impact on these processes is reflected in an individual's communication via coupled mechanisms: vocal articulation, facial gesturing and choice of content to convey in a dialogue. In particular, MDD-induced neurophysiological changes are associated with a decline in dynamics and coordination of speech and facial motor control, while neurocognitive changes influence dialogue semantics. In this paper, biomarkers are derived from all of these modalities, drawing first from previously developed neurophysiologically motivated speech and facial coordination and timing features. In addition, a novel indicator of lower vocal tract constriction in articulation is incorporated that relates to vocal projection. Semantic features are analyzed for subject/avatar dialogue content using a sparse coded lexical embedding space, and for contextual clues related to the subject's present or past depression status. The features and depression classification system were developed for the 6th International Audio/Video Emotion Challenge (AVEC), which provides data consisting of audio, video-based facial action units, and transcribed text of individuals communicating with the human-controlled avatar. A clinical Patient Health Questionnaire (PHQ) score and binary depression decision are provided for each participant. PHQ predictions were obtained by fusing outputs from a Gaussian staircase regressor for each feature set, with results on the development set of mean F1=0.81, RMSE=5.31, and MAE=3.34. These compare favorably to the challenge baseline development results of mean F1=0.73, RMSE=6.62, and MAE=5.52. On test set evaluation, our system obtained a mean F1=0.70, which is similar to the challenge baseline test result. Future work calls for consideration of joint feature analyses across modalities in an effort to detect neurological disorders based on the interplay of motor, linguistic, affective, and cognitive components of communication.
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Summary

Major depressive disorder (MDD) is known to result in neurophysiological and neurocognitive changes that affect control of motor, linguistic, and cognitive functions. MDD's impact on these processes is reflected in an individual's communication via coupled mechanisms: vocal articulation, facial gesturing and choice of content to convey in a dialogue. In...

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Detecting depression using vocal, facial and semantic communication cues

State of the art focal plane arrays of InP/InGaAsP Geiger-mode avalanche photodiodes for active electro-optical applications

October 10, 2016
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Conference Paper
Author:
Jonathan P. Frechette
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Published in:
2016 MSS Active E-O Systems, 10 October 2016.
Topic:
ladar
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R&D group:

Summary

MIT Lincoln Laboratory has developed InP/InGaAsP Geiger-Mode Avalanche Photodiodes and associated readout integrated circuits (ROICs) that have enabled numerous active optical systems over the past decade. Framed and asynchronous photon timing ROIC architectures have been demonstrated. In recent years, efforts at MITLL have focused on technology development to advance the state of the art of framed Gm APD FPAs and a 256x128 pixel FPA with on-chip data thinning has been demonstrated.
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Summary

MIT Lincoln Laboratory has developed InP/InGaAsP Geiger-Mode Avalanche Photodiodes and associated readout integrated circuits (ROICs) that have enabled numerous active optical systems over the past decade. Framed and asynchronous photon timing ROIC architectures have been demonstrated. In recent years, efforts at MITLL have focused on technology development to advance the...

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State of the art focal plane arrays of InP/InGaAsP Geiger-mode avalanche photodiodes for active electro-optical applications

Effects of humidity and surface on photoalignment of brilliant yellow

October 9, 2016
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Journal Article
Author:
Junren Wang
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Published in:
Liquid Cryst., Vol. 44, No. 5, 2017, pp. 863-72.
R&D area:
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Summary

Controlling and optimising the alignment of liquid crystals is a crucial process for display application. Here, we investigate the effects of humidity and surface types on photoalignment of an azo-dye brilliant yellow (BY). Specifically, the effect of humidity on the photoalignment of BY was studied at the stage of substrate storage before coating, during the spin-coating process, between film coating and exposure, and after exposure. Surprising results are the drastic effect of humidity during the spin-coating process, the humidity annealing to increase the order of the BY layer after exposure and the dry annealing to stabilise the layer. Our results are interpreted in terms of the effect of water on the aggregation of BY. The type of surface studied had minimal effects. Thin BY films (about 3 nm thickness) were sensitive to the hydrophilicity of the surface while thick BY films (about 30 nm thickness) were not affected by changing the surface. The results of this paper allow for the optimisation of the BY photoalignment for liquid crystal display application as well as a better understanding of the BY photoalignment mechanism.
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Summary

Controlling and optimising the alignment of liquid crystals is a crucial process for display application. Here, we investigate the effects of humidity and surface types on photoalignment of an azo-dye brilliant yellow (BY). Specifically, the effect of humidity on the photoalignment of BY was studied at the stage of substrate...

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Effects of humidity and surface on photoalignment of brilliant yellow

Use of Photoacoustic Excitation and Laser Vibrometry to Remotely Detect Trace Explosives

October 6, 2016
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Journal Article
Author:
Charles M. Wynn
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Published in:
Applied Optics, vol. 55, no. 32
Topic:
chemical technologies
R&D area:
R&D group:

Summary

In this paper, we examine a laser-based approach to remotely initiate, measure, and differentiate acoustic and vibrational emissions from trace quantities of explosive materials against their environment. Using a pulsed ultraviolet laser (266 nm), we induce a significant (>100  Pa) photoacoustic response from small quantities of military-grade explosives. The photoacoustic signal, with frequencies predominantly between 100 and 500 kHz, is detected remotely via a wideband laser Doppler vibrometer. This two-laser system can be used to rapidly detect and discriminate explosives from ordinary background materials, which have significantly weaker photoacoustic response. A 100  ng/cm2 limit of detection is estimated. Photoablation is proposed as the dominant mechanism for the large photoacoustic signals generated by explosives.
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Summary

In this paper, we examine a laser-based approach to remotely initiate, measure, and differentiate acoustic and vibrational emissions from trace quantities of explosive materials against their environment. Using a pulsed ultraviolet laser (266 nm), we induce a significant (>100  Pa) photoacoustic response from small quantities of military-grade explosives. The photoacoustic signal...

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Use of Photoacoustic Excitation and Laser Vibrometry to Remotely Detect Trace Explosives

Application of a resilience framework to military installations: a methodology for energy resilience business case decisions

October 4, 2016
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Technical Report
Author:
Nicholas M. F. Judson
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Published in:
MIT Lincoln Laboratory Report TR-1216
Topic:
energy systems
R&D area:
R&D group:

Summary

The goal of the study was to develop and demonstrate an energy resilience framework at four DoD installations. This framework, predominantly focused on developing a business case, was established for broader application across the DoD. The methodology involves gathering data from an installation on critical energy load requirements, the energy costs and usage, quantifying the cost and performance of the existing energy resilience solution at the installation, and then conducting an analysis of alternatives to look at new system designs. Improvements in data collection at the installation level, as recommended in this report, will further increase the fidelity of future analysis and the accuracy of the recommendations. And most importantly, increased collaboration between the facility personnel and the mission operators at the installation will encourage holistic solutions that improve both the life cycle costs and the resilience of the installation's energy systems and supporting infrastructure.
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Summary

The goal of the study was to develop and demonstrate an energy resilience framework at four DoD installations. This framework, predominantly focused on developing a business case, was established for broader application across the DoD. The methodology involves gathering data from an installation on critical energy load requirements, the energy...

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Application of a resilience framework to military installations: a methodology for energy resilience business case decisions
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